Adult stem cells hold great promise for regenerative medicine, tissue repair and for the study of early developmental events. The identification of new sources of insulin-producing cells would potentially give rise to novel treatment options for patients suffering from diabetes in all its forms. In response to partial pancreatectomy or physiologic stimuli, pancreatic [unreadable] cells can regenerate by replication of existing [unreadable] cells and by [unreadable] cell neogenesis. Pancreatic progenitor/stem cells (PPSC) have been postulated to be the cellular origin of neogenesis, though their existence remains controversial. We hypothesize (1) that a population of PPSC exists, which express telomerase (mTert) as a marker of their stem cell phenotype, (2) that PPSC can be isolated and expanded using mTert-GFP transgenic mice and (3) that with transplantation their differentiation will recapitulate normal islet cell development. We have used an innovative method to generate transgenic mice with endogenous stem cells labeled with GFP. We currently have two independent mTert-GFP transgenic mouse lines, from which GFP+ cells are being evaluated for their stem cell potential. Validation studies in bone marrow and testis have demonstrated GFP expression within two adult stem cell populations: hematopoietic stem cells and male germ cells. In addition, this model has allowed for the identification and isolation of a putative intestinal stem cell population, as defined by the ability of GFP+ intestinal crypt cells to specifically engraft the intestinal stem cell niche following blastocyst injection and to persist long-term in adult chimeric animals. Recent studies in pancreas, following short-term Exendin-4 stimulation, demonstrate an inducible population of GFP+ cells using both FACS analysis and immunohistochemistry (IHC) in both lines of mice. GFP expression is localized to cells within ductal structures and is absent from islets and acinar cells. This proposal aims to validate the identity and developmental potential of GFP+ putative pancreatic progenitor/stem cells isolated from mTert-GFP transgenic mice. Specifically, we will use in vitro and in vivo model systems, e.g., cell culture, transplantation and blastocyst injection, to establish the potential of these cells to develop into insulin secreting cells. In addition, we propose lineage-tracing studies, using mTert-CreERT2 transgenic mice, to further study the developmental potential of mTert expressing cells in adult pancreas. Type I Diabetes is a major cause of human suffering and results from the destruction of pancreatic beta cells and the loss of insulin production. The ultimate treatment for this condition will involve (1) reversal of the destructive autoimmune attack on beta cells and (2) regeneration of normal beta cells. The identification of new sources of insulin producing cells would have an enormous impact on the future of patients with this disease and on the health care system. Our proposal uses an innovative new model to search for pancreatic progenitor cells in mice with the goal to identify these elusive cells. [unreadable] [unreadable] [unreadable]